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Last time, I talked about dark energy, how it was recently discovered, and how it makes up the missing 69 per cent of the 'energy budget' of the universe.

Now, you might have come across the concept that the universe is expanding. What dark energy does is make the expansion accelerate — so today the universe is expanding at a rate about one-quarter times faster than it was five billion years ago.

Back in the 1920s, the astronomer Edwin Hubble announced his discovery that the universe was expanding. The galaxies were moving further apart.

Hubble used the new 100-inch Mount Wilson telescope to look at galaxies. He measured their doppler shift. That's the change in frequency, due to the speed of the galaxy. He found that practically all galaxies were moving away from us. This shifted the colour of their light towards the red end of the colour spectrum — hence the phrase, 'red shift'. Hubble also found that the further away a galaxy was; the bigger was its red shift.

Since the 1920s, the astronomers assumed, thanks to gravity doing its 'sucking' thing that this expansion would mellow and slow down.

But in May 1998, cosmologists held a conference called The Missing Energy in the Universe. Some of them presented their data showing that the universe had strangely increased its rate of expansion, about five billion years ago and, as a result, the universe was bigger and emptier than we previously thought.

Of the 60 scientists at the conference, 40 accepted the revolutionary new findings. Now, this was very unusual. Generally, a poll is not taken at scientific meetings asking if the scientists do or do not accept a result. The science of 'dark energy' was just beginning — like a baby.

But, how did astronomers measure that the universe was expanding at a decreasing rate until about five billion years ago and then it gently began to expand at a faster rate?

Answer — they used 'exploding stars' as a 'standard candle'.

Exploding stars? What are they?

Well, there are a few different mechanisms by which stars can explode. Our astronomers looked at type 1a supernovae, which start off as a 'white dwarf'.

Now, a white dwarf is a 'degenerate' star that has finished its 'normal' burning, and is now in the later stages of its life. This stage is the common end point of evolution for stars that started off with a mass between eight and 10.5 times greater than the mass of our Sun. The star has now cooled down and collapsed. It's about the size of our Earth, but has roughly the mass of our Sun, so it's very dense (about one tone per mil). There are about eight white dwarfs in the nearest 100 star systems.

To make a type 1a supernova, imagine that a white dwarf and a big star are in a tight orbit around each other. The white dwarf 'sucks' some hot gas from the bigger star onto its surface. Once this layer gets a metre-or-two thick and the white dwarf reaches a mass of about 1.38 times the mass of our Sun, the whole star explodes, like a giant hydrogen bomb.

The white dwarf erupts outwards at about five to 20,000 kilometres per second. After three weeks, the explosion reaches about 10 billion times the brightness of our Sun and then it fades over the next few months. These supernovae are all close to the same brightness, because they all explode at around the same mass.

Now, I mentioned 'standard candle'? What is that? Well, a standard candle is something that has a fixed and known brightness.

You see, a major part of astronomy is measuring the distance to stars and galaxies and the like. But, how do you tell the difference between a faint star that is close and a bright star that is distant? After all, to your naked eye, they each have the same brightness.

Luckily, type 1a supernovae all pretty well reach the same maximum brightness. So, if it's bright, it's close, and if it's faint, it's far away. This is how a type 1a supernova can make a reasonable standard candle. We can measure their actual distance by their brightness and the red shift will give us their supposed distance.

Two separate teams of astronomers measured many type 1a supernovae. The younger and closer ones were where they expected them to be, but the older and more distant ones were not. They were fainter and further away. It was as though the expansion rate of the universe had sped up about five billion years ago.

The astronomers were seeing the fingerprint of dark energy — the missing 69 per cent of the universe. So, next time, I'll talk about why dark energy made the expansion of the universe increase — and what it will do in the future …

JoeBloggs :

Dave Grimes :

14 Aug 2013 12:58:25am

Hi Dr K,I'm a big fan and love the shirts! My question is;where does the current thinking lie on Super-Chandrasekhar type 1a supernovae? For background dear readers... These are odd 1a supernova where the white dwarf is much heaver than 1.38 solar masses, something the brilliant astrophysicist Subrahmanyan Chandrasekhar ruled out mathematically and unsurprisingly is called the Chandrasekhar Limit. While these super-1a supernovae are rare they may just be frequent enough to skew the data away from being a reliable standard candle. Today is there a consensus on the causes and identification of these oddities?

Volker vHunnius :

whatdoctor :

14 Aug 2013 3:17:23pm

I like to believe the dark energy is extra space being created as objects move away from one another. Sort of like holes being ripped in the fabric of space. When the Universe was smaller, gravity was able to counter this effect to some extent - but now it has run away and should keep on accelerating.

Peter :

BacterialOverlords :

26 Aug 2013 5:04:45pm

The original star will reach the end of its life and swell up to become a red giant. Then, if unable to fuse carbon, this will build up at the core and after the outer layers of the star form a nebula the inner core which forms the white dwarf. Now, the reason it is so small is because the white dwarf is no longer supported by the heat generated by fusion, only by what is called electron degeneracy pressure (each electron must be discrete, and therefore resists being pushed closer together). So you get high mass with small size. Neutron stars are similar except this time it the neutrons that resist degeneracy (quantum degeneracy pressure.) If you dropped something from one meter onto a neutron star it would hit it travelling around 2000 kilometres per second!!. Our universe is truly amazing. Sorry to ramble, hope that answered your query.

Richard Guse :

15 Aug 2013 1:31:32am

Have we directly observed a spectrum shift over time due to the universal accelleration? I realize that the change may be below our threshold to detect in the limited time we've had detailed spectra, but it would be a nice thing to see validated as I'm not entirely comfortable with the conclusions based on standard candles - its nagging me that there many be other explanations and seeing the spectra change over time would be a shiny nail.

M J Murcott :

JoeBloggs :

15 Aug 2013 1:55:30pm

Hi Dr Karl,

I note that Laura Mersini-Houghton, theoretical physicist at the University of North Carolina at Chapel Hill, and Richard Holman, professor at Carnegie Mellon University, predicted that anomalies in radiation existed and were caused by the pull from other universes.

They suggest that the cosmic map of background radiation data gathered by Planck telescope provides evidence of the existence of the multiverse, concluding that it shows anomalies that can only have been caused by the gravitational pull of other universes.

Is there any chance you can include a discussion on this in the next part (or in another article?).

whatdoctor :

17 Aug 2013 6:13:48am

An interesting idea. If the other Universes were evenly distributed, then the net effect of their gravity would be zero. If they are not evenly distributed. the acceleration would be distorted in smoe directions. Also they may be so far away that their gravity effect is negligible (less than one quantum of energy on the entire Universe.

What if some of them are made of anti-matter? I think gravity still works the same on antimatter. Gotta love this stuff.

BacterialOverlords :

26 Aug 2013 5:11:36pm

How does the concept of distance relate to other universes? What is between them for gravity to act on? Can you even talk about "between" universes? Why would one universe affect another? What if they occupy the same "space"? I find it unlikely that, if there is a multiverse, one universe would gravitationally affect another. Ready to be convinced though!

Help101 :

04 Sep 2013 10:59:17am

How does the concept of distance relate to other universes? - It is entirely artificial in the Many Worlds theory as there is no distance between them. In other multiverse theories however the distance could be measure in terms of distance within a higher dimensionality as such the Bulk.

"Why would one universe affect another?" - Some theories suggest that gravity permeates accross universes which would enable other universes to impact on this one. Also some multiverse theories suggest that universes can collide and/or interact within the Bulk thus impacting on this universe.

Ted Krol :

20 Aug 2013 10:06:39am

I have read a number of articles suggesting that everything in the universe spins; from the atomic level all the way to the galactic level. Therefore, is it probable that the universe itself is also spinning? The theory was based on observations of galaxies spinning in the same direction when observed from directions 180 degrees apart. That is all spinning clockwise in one direction and all spinning anticlockwise in the opposite direction for example. If the universe is truly spinning, that would indicate that galaxies must be travelling at different speeds depending upon how far they were from the spin axis. Could the different speeds that galaxies are travelling at account for the red shift we observe? Furthermore, if our position (observation point) is constantly changing as our solar system rotates in our own galaxy do we have a reliable reference point? Perhaps the universe is not expanding at all!

Help101 :

22 Aug 2013 8:48:14am

If the universe is truly spinning, then the question must be ask, what is it spinning in relation to? It would need to be spinning in relation a higher dimensionality.

For example if you were in 'empty' space with no reference point (ie. anything to see, and all matter etc was removed) and you were spinning you would still feel the sensation of spinning because you are spinning in relation to space/time itself. The same would apply to a universe that is spinning.

Ted you ask "If the universe is truly spinning, that would indicate that galaxies must be travelling at different speeds depending upon how far they were from the spin axis." Which isn’t the case, for there to be a spin axis there would need to be a centre of the universe, however there is no centre of the universe because there is no centre to the expansion, it is the same everywhere.

The Big Bang should not be visualised as an ordinary explosion. The universe is not expanding out from a centre into space, rather, the whole universe is expanding and it is doing so equally at all places. Try not to visualise our universe in just 3 dimensions.

The analogy of a balloon with a large number of dots marked on its surface is a good explanation of expansion. If the balloon is blown up the distances between the dots increase in the same way as the distances between the galaxies.

It is important to appreciate that 3 dimensional space is to be compared with the 2 dimensional surface of the balloon. The surface is homogeneous with no point that should be picked out as the centre (ie. if you look at the surface of a ball and I asked you to point to the central part of the surface you couldn’t as everywhere on the surface of a ball is ‘central’). The centre of the balloon itself is not on the surface, and therefore should not be thought of as the centre of the universe or even part of the universe as such. If it helps, you can think of the radial direction in the balloon as time. It is better to regard points off the surface as not being part of the universe at all.

BacterialOverlords :

26 Aug 2013 5:15:23pm

Love the analogy. Esp the part about the radial dimension representing time. If space is stretching, then time must be too. What will happen as we get closer to the big rip? Will time start to become ripped? Streched, disjointed?

Help101 :

28 Aug 2013 10:10:53am

I've read concepts that as the universe continues to inflate time itself will also stretch to the point that time will become meaningless as space and time are inseperable, particularly in 10 to the power of 150 years time when the universe is 'empty' and approaching heat death.

They also suggested that the physics of the universe will be very different then as well.

The really interesting thing about time is the non linear nature of it, and that the slit experiments involving photons suggest that time is also a factor of other dimensions of this universes (beyond the standard 3+1 when examining when the wave function finds out, in the past, that it will decohere in the future upon observation.

The explanation being something along the lines that the time component of the decoherence is linked via another dimension(s), ie. there is a level of entanglement with itself spread over time via another dimension. A the time the wave function arrives at the slit the future observed decohered photon 'tells' the wave function where to decohere in the future (when it reaches the point of observation).

Bazza :

03 Sep 2013 1:54:55am

So if we learn to time travel (using a time machine made of slits) will we disintegrate in a shower of decohered photons? I have some friends who do that when they drink! They certainly like to be observed, so I guess if we don't look they just might make sense. You think?

The universe appears to have increased its expansion about 5 billion years ago so it seems to correlate with the time our Solar System began to form. It may be that the universe saw our system come into existence, extrapolated the future presence of humans and politicians and decided to run away. Dark matter is just the exhaust from their getaway cars!

Bazza :

03 Sep 2013 2:20:37am

So explain why so many astronomers etc talk about the origin of the universe as a point of compressed material that explodes as the Big Bang. They can not both be correct. The whole myth is pure conjecture at this stage anyway. If your concept is to be accepted then the language used and the fundamental assumptions of initial state need to be reviewed. Just as the speed of light is questioned by the concept of a point of origin of compressed matter leading to an expanded Universe. It can not expand at the required rate to create the universe in the given time given the speed limit.

Also to deny there is no ‘centre’ to our Universe requires better explanations. We can only see a limited amount of the universe and so can not categorically say we know and understand its structure. Imagine if it goes many, many more times in diameter. The gravity of that additional mass may be drawing our local sector of the Universe outwards in all directions so adding to the expansion as well. I haven’t pursued this thought before so feel free to tear it apart with as much evidence as you can muster. And stay away from balloons – they tend to go POP! Just like the Big Bang I guess.

It is annoying when explanations resort to whimsical references to alternate or additional dimensions or universes to avoid the unknown rather than simply saying "we don't know - Yet". Using abstract twists in mathematics to offer "proof" is just as unconvincing. Those authors should admit their concepts are as much just Sci-Fi and fiction as anything else for now, entertaining and wonderfully thought provoking, but that's all. YET.

Help101 :

04 Sep 2013 11:22:08am

Bazza,

Astrophysicists have never described the big bang as an explosion in the regular sense. It is simply an inflation. It didn't expand out from a single point as an explosion would, everything within the singularity inflated (largely uniformly). Try not to think of the balloon popping, but rather the balloon inflating. For example all of the balloon existed as the singularity, the singularity is just in a different shape (a less condensed form in terms of the space/time it occupies relative to itself).

You are of course welcome to accept or reject the science in relation to the inflation of the universe and/or the various fields that consider the reality of a multiverse.

A while back Brian Greene pointed out that some scientists think we might just be able to find evidence for a multiverse. They propose that if our universe and another were born close together, the two might have collided. That collision could have left its own fingerprint (ripples in the cosmic background radiation, the heat left over from the Big Bang).

Laura Mersini Houghton, theoretical physicist at the University of North Carolina at Chapel Hill, and Richard Holman, professor at Carnegie Mellon University, predicted that anomalies in radiation existed and were caused by the pull from other universes in 2005. Now that she has studied the recent Planck data, Dr Mersini Houghton believes her hypothesis has been proven.

It is also perhaps worth remembering that mathematics predicted the existence of things we now take for granted well before we could obverse them. Black Holes being an excellent example. I wouldn't knock the math just yet, there are after all great truths to be found within it.

Alex :

27 Aug 2013 3:00:39pm

If the universe (or at least the bit we can see) is expanding and this expansion is accellerating, shouldn't things be dissappearing behing the event horizon? Can we not see today things that we could see yesterday and is this a valid prediction of the theory?

Jan Willem :

01 Sep 2013 11:41:49am

We don't truly know. The only measure we have is how fast other star systems move away from and to the Milky way.Since the start of this universe comes from one single point we will never be able to tell if it started within another universe we are at present a part of.

Help101 :

03 Sep 2013 9:04:41am

It will be interesting to see how this is examined in the future and whether it would be possible to know for certain whether everything in this universe can be seen on the event horizon of this universe (as in the holographic principle) and whether that is itself the event horizon of a white hole.

Vince :

03 Sep 2013 11:47:03pm

The red shift of light from a distant galaxy indicates the light has lost energy. That can be due to moving away or any other factor that can lower the energy of light. If space is curved energy may be lost taking the curve. it takes energy to move in a curve but not to go in straight line. How many other factors can reduce the energy in a photon?

Help101 :

05 Sep 2013 8:55:42am

Vince,

When a photon moves in space it travels in a straight line.

Even when it encounters a warp in space/time it still travels in a straight line across the curvature of the warp. It may appear to us that the photon has taken a curve and has therefore changed its trajectory but in reality it is travelling dead straight (while following the curvature of warp).

The photon doesn't lose energy, the energy is just spread out more, ie. the wave of the photon (as in its wave function) becomes less condensed.